As shown in FIGS. 1 and 2, in the prior art, a coil around a magnetic material is used to generate magnetic field that “adds” up inside the magnetic material by using the same biasing current. The direction of flow of current in the top layer is opposite in the z-axis to that of the bottom layer, but the field lines below the top metal layer and above the bottom metal layer are confined in the magnetic field and will be along the same direction.